HOW PLANTS ARE INFLUENCED 



349 



well shown in Fig. 203. It may be observed in vines, 

 etc., which climb on walls. 



The effect of wind in drying up the blossoms of 

 fruit trees, etc., is 

 well known. For this 

 reason, and also be- 

 cause the winds 

 lower the tempera- 

 ture and do consid- 

 erable damage to 

 trees laden with ice 

 and snow,- the use of 

 windbreaks is often 

 indispensable. 



FOOD. We have 

 already learned 

 (pages 137 to 162) 

 that the kind of min- 

 eral food the plant 1 

 receives affects its 

 growth and general 

 appearance . Thus, 

 abundance of nitrogen 2 causes a particularly strong, 



1 See articles by Riley and by Woods in the Year Book of the U. S. Depart- 

 ment of Agriculture for 1901. 



2 It is an interesting fact that abundant manuring with nitrogen, combined 

 with abundant watering, very commonly produces "green flowers," i. e., flowers 

 in which petals, stamens and even ovules are transformed into green leaf- like 

 bodies. This happens frequently in garden Asters and other Compositae. In 

 some cases this greening of the flowers is caused by the attacks of plant-lice. 



202. The effect of wind; branches stunted 

 and killed on the windward side. 



